[clang] [Clang][OpenMP] Fix crash on `atomic` with an erroneous statement (PR #228914)

[Oliver Hunt via cfe-commits]

https://github.com/ojhunt requested changes to this pull request.

Super sorry for the delay - I did a review but forgot to actually submit it.

I _think_ there's an impact on follow on diagnostics with your change

https://github.com/llvm/llvm-project/pull/228914